The present invention relates to seating and, in particular, to a chair control having a tension adjustment mechanism. Articulated seating, such as tilt back chairs, and other furniture articles of the type having at least two, mutually adjustable portions, are used extensively in office environments. The mutually adjustable portions of the seating are normally interconnected by a controller or control, which mechanically adjusts the mutual orientation of the various adjustable seating portions. Seating controls normally include springs which bias the seating into a normal or upright position. The controls also typically include some type of adjustment device to vary the biasing force which resists movement of the adjustable portions of the seating from their normal position.
Synchrotilt chair controls provide a mechanism which causes the chair back to rotate at a rate different from that of the chair bottom or seat. Such mechanisms are generally referred to as "synchrotilt" controls, since the chair back and chair bottom move in a synchronous fashion. Normally, synchrotilt controls cause the chair back to tilt at a faster rate than the chair bottom, so that the user tilts the chair back rearwardly, the user's feet are less likely to be lifted off of the floor by the rising front edge of the chair bottom.
Chair controls are normally mounted below the chair bottom, so that they do not interfere with the use of the chair, and so that they do not detract from the aesthetics of the chair design. As a result, the axis about which the chair back and chair bottom rotate with respect to each other, which is referred to herein as the "common axis" or the "synchrotilt axis," is also disposed below the chair bottom.
Prior synchrotilt chair controls, such as that disclosed in U.S. Pat. No. 4,390,206, entitled SYNCHROTILT CHAIR CONTROLS, which issued on Jun. 28, 1983, to Faiks et al., have a rather complicated construction, and are rather large and bulky. Such devices have a tow-part articulated iron construction, with a fixed axle about which back and seat support portions of the iron rotate. The control is completely separate or independent from the chair or shell, and mutually rotates the chair back and chair bottom about the fixed axle, which is located below the chair bottom. The chair includes a tension adjustment for setting the initial preload of a torsion back which biases the seat back to an upright position.